I think this is a very good way to understand namarupa using the six senses.
SA298 defines namarupa as form, feeling, perception, activities, consciousness while SN12 .2 defines it as form, feeling, perception, volition, contact, attention. I think the reason SA298 defines namarupa that way is because the author or translator may think namarupa should be a being while we do not find that in SN12. 2. Since I do not see namarupa as a fetus or a being, I choose the definition in SN12. 2. because if namarupa is a being then external namarupa must be an external being and it will conflict with SN12. 19.
From SN12.19, we have:
“this body and external name and form. Contact depends on this duality.”
The body and the external namarupa are the duality that causes the arising of contact. The body here works with the external namarupa for contact to arise, so we can say that this is the physical body that provides the physical senses for the operation. We also know that:
In dependence on the eye and forms, eye-consciousness arises. The meeting of the three is contact.
So, this external namarupa is the object of the six sense bases. Therefore, they are external form, sounds, odours, tastes, tactile objects, mental phenomena.
Since we have an external namarupa, we can infer that there is non-external namarupa. Otherwise, the “external” is meaningless. Let’s assume that the internal namarupa is the reflection of the external namarupa in our mind. If this is the case, we can say that the internal namarupa is the internal form, sounds, odours, tastes, tactile objects, mental phenomena in our mind. This internal namarupa could be the namarupa in DO. In fact, what we are experiencing is actually the reflection of the external objects out there. We do not directly see the object. We actually see the reflection of the object in our mind.
To map this internal namarupa with its definition in DO, we can take nama (feeling, perception, intention, contact, attention) as internal mental phenomena, and rupa (earth, water, fire, air and the form derived from them) as internal form, sounds, odours, tastes, tactile objects. This internal rupa is the reflection of the external rupa in our mind, so it is also mental.
However, nama in DO must have intention; therefore, namarupa in DO should be the intentional reflection of the external namarupa. This intention is driven by ignorance; therefore, the namarupa in DO is not simply the reflection of the external namarupa, but it is the intentional reflection of the external namarupa. This is important because we can also have the reflection of external namarupa without intention. In this case, this reflection is not namarupa of DO. The cessation of namarupa in DO is the cessation of the intentional reflection of external namarupa, not the unintentional reflection. This shows that we can still experience the world even if the namarupa in DO ceased.
My previous understanding of namarupa in DO is quite close to this, but it is not very clear. I was thinking namarupa is the connection between nama and rupa or between the mind and its objects. The connection obviously must be done through the six senses, and that is this reflection of the external namarupa. We can also see this connection in SN12.19 as the contact that depends on the body and the external namarupa.
I think this reflection of external namarupa in DO does not happen all at once for all the senses, but it is gradual filling as I previously explained in my example
This filling will trigger the arising of all the appropriate senses for the experience, and they will eventually be reflected in the mind. Therefore, in DO we can see the six senses after namarupa. These six senses in DO are the type of the reflection of the external namarupa. Therefore, they are not the physical six sense bases. They arise depending on the intentional reflection of appropriate types of external namarupa. Without that, they will not arise.
To me, I think this is another very good way to understand namarupa. Without understanding namarupa, we will not be able to understand DO.
My understanding is limited, so I may have some mistakes that I cannot see. Feel free to validate my understanding. I am happy to correct them. Of course, this is just my own limited view.